Imagine if your parents were 300+ years old. What kind of assets would they have accrued? How well connected are they compared to humans? What kind of accumulated life learnings would they have?
I mean, I think there's no possible way the culture of elves could be the same nearly-Ferengi human culture you're describing (i.e. the kind that concerns itself with "accruing assets"). Nor I think, given war, disease, monsters, revolutions, apocalypses and so on, would even elves actually be able to hold on to that wealth for hundreds and hundreds of years. Further, even in "elven enclaves" it seems like there's usually relatively little trade in non-perishable goods or resource exploitation (which would make sense).
It's like you're imagining immortal greedy 1800s-2000s humans time-travelling to the 1100s and carefully "accruing assets" like they were vampires planning to live forever.
I think most very long-lived beings probably couldn't live that way, wouldn't want to live that way, would rapidly come to see that such assets are worthless and ephemeral.
Also what connections? Most of their "connections" would be dead. Only other elves and similar, who are presumably pretty limited in number would be a thing - and the whole "all elves know each other" thing has been considered at length by fantasy. Plus just because you know someone, doesn't mean they like you or want to help you. The sort of feuds that could fester for centuries could be staggering.
Accumulated life learnings would be a thing, but again, it'd be complex because they'd have such a wealth of history that filtering signal from noise might be pretty challenging, and a lot of stuff that might have made sense 500 years ago might be outdated today. I think the main thing they'd learn would probably be to live for the now, not to dwell on the past which would lead to stagnation and wallowing, or to obsess about the future, which they'd know was ever in flux (and also tends to get you killed if you get too involved in it!).
I think what you're really pointing out here is that for super-long-lived beings they probably couldn't be very human-like past their first couple of hundred years.
Now imagine that you were physically mature at 25 but spent the last 75yrs as a "minor" (non-adult) where your parents could manage your finances. What kind of "housewarming" gifts might you receive from parents that spent collecting your nickels and quarters to buy stocks, bonds, land, or just flatware, dishes, furniture, horses, etc?
This is a purely 20th century and later thing (or late 1800s at earliest, but even then the vast majority of people didn't live like that). It simply isn't how the world worked before that. Backprojecting it to elves in a quasi-medieval society or the like makes no sense. You're conceptualizing the world elves live in as if it's like, somewhere between the 1890s and the 1940s in the USA, it seems.
Of course culture could mean the tween-elf earnings go to the parents, so what if a married couple had a minimal cost laborer for 7 decades?
I mean, slaves existed. We know how much/little economic impact they had. You still have to feed/clothe/house them, especially if you like them. No married couple got rich off a single unskilled slave. There's a reason people trying to make money off slaves, whether in ancient Rome, or the US pre-Civil War South, usually needed to have quite a lot of them. Otherwise they're basically just cheaper servants, and overall exert an economic cost, rather than making you money (with rare exceptions like highly skilled slaves - but historically they tended to get paid themselves and sometimes quite well!).
You seem to be thinking this is capitalism and this would just be a nice little guy making gold coins appear in your pocket. Unlikely. Elves aren't Ferengi. People don't generally keep personally scrabbling for wealth when they don't need to (greedy billionaires aren't scrabbling, note - most of them are pretty lazy and it's just wealth begets wealth under modern free-market globalised capitalism - but fantasy settings generally aren't under free-market globalised capitalism, they're under pre-capitalistic situations). More likely long-lived elves quickly realize how futile and grim that is, and what really matters is living life.